The invention relates to a semiconductor device comprising a semiconductor body which is provided at a surface with a first field effect device comprising a source region, a surface-adjoining channel region and a gate electrode located above the channel region and separated from this region by an insulating layer, a second field effect device being present in the semiconductor body in the form of a transistor comprising a source region, a drain region and an intermediate channel region with a gate electrode insulated from the channel region.
The first field effect device can then be constituted by an insulated gate field effect transistor which is connected as a current source. In another important embodiment, the first field effect device constitutes the input stage of a charge-coupled device. The second field effect device, which in both embodiments is constituted by a field effect transistor, can be considered as a resistor. When a current is passed through this transistor, a voltage is generated which is supplied to the first field effect device.
The value of this voltage is generally critical, as will appear from the embodiments to be described. This value may be adjusted, for example, by means of the value of the current which is passed through the second field effect transistor. The usability of this method is very limited, however, because the current soon becomes too large, as a result of which the dissipation becomes too large or too small, so that inertia effects will occur. It is also known to control the resistance through the transistor by means of the threshold voltage. The usual manner of threshold voltage adjustment is to control the doping in the channel region by means of ion implantation. However, in this case a separate implantation step is required, which results in the process becoming more complicated. Moreover, the spread in the threshold voltage is fairly large with the use of this method, i.e. according to the prior art on the order of 100 mV.